Extracellular molecules produced by S. mutans and implicated in the formation of cariogenic dental plaque are glucosyltransferase, dextranase, lipoteichoic acid, and fructosyltransferase. Investigations of the interactions of these molecules with serum and saliva, antibodies, dental plaque fluid, hydroxyapatite, cariostatic agents, and fluoride have partially elucidated their roles in plaque. Immunization of rodents and monkeys with purified preparations of these molecules has led to antibody formation. Protection against infection by S. mutans is being evaluated. Preliminary experiments which measured these S. mutans molecules in dental plaque fluid from monkeys suggest a correlation between GTF activity and the presence of S. mutans in plaque. These studies are designed to gain insight into the biochemical and immunological aspects of dental caries which will lead to a rational approach for the control of this disease.